docs(architecture): spec alknet-core with per-crate subdocs, ADR-010/011

Add alknet-core architecture specs in docs/architecture/crates/core/ with
focused subdocuments for core types, endpoint, auth, and config. Write
ADR-010 (ALPN Router and Endpoint) defining AlknetEndpoint, HandlerRegistry,
accept loop, and graceful shutdown. Write ADR-011 (AuthContext Structure)
defining AuthContext fields, immutability in handle(), and IdentityProvider
injection pattern. Resolve OQ-04 (static registration), OQ-12 (file paths
only for v1). Add OQ-11 (auth observability). Fix remaining alknet-secret
references to alknet-vault across ADRs 003/004/005/009.

docs/architecture/decisions/009-one-way-door-decision-framework.md

@@ -8,7 +8,7 @@ Accepted
 
 Not all architectural decisions carry the same reversal cost. Some decisions are easy to change later — if you pick the wrong data structure, you refactor. Other decisions are nearly impossible to reverse — if you build a type hierarchy that forecloses WASM compatibility, every handler written against that hierarchy must be rewritten.
 
-This distinction matters especially during Phase 0 (exploration) and early Phase 1 (architecture). The project is post-pivot with foundational ADRs in place but no implementation code yet (except alknet-secret). Decisions made now shape the API surface that every handler depends on.
+This distinction matters especially during Phase 0 (exploration) and early Phase 1 (architecture). The project is post-pivot with foundational ADRs in place but no implementation code yet (except alknet-vault). Decisions made now shape the API surface that every handler depends on.
 
 Without an explicit framework, one-way doors can be treated as casually as two-way doors, leading to costly rework. Or conversely, two-way doors can be over-analyzed, blocking progress on decisions that are cheap to reverse.